__Motivation__
`Http2FrameCodecBuilder` constructor calls `server()` internally which disallows using certain methods on the builder later. Additionally, the constructor is package private which limits extension of the `Builder` as well as usage outside the available `forClient()` and `forServer()` static methods.
__Modification__
- Introduce a `public` no-arg constructor to `Http2FrameCodecBuilder`.
__Result__
`Http2FrameCodecBuilder` can now be used to create the codec with `Http2Connection` or `Http2ConnectionDecoder` and `Http2ConnectionEncoder` which was earlier not possible due to implicit call to `server()` by the `Http2FrameCodecBuilder` constructor.